3. Results
3.1. Cultivation of CHO-S cells in bioreactor Growth curves and viability are shown in Fig. 2. Growth rate during log phase in a bioreactor with reciprocal mixing was not significantly different from that in a bioreactor with rotary mixing, namely 6FT or EE. Cell density in all bioreactors reached approximately 6.0 × 106 cells/mL, with no significant difference across them all (Fig. 2B). This implied that the mixing methods (rotary or reciprocal) did not affect the growth rate during log phase or the cell density achieved after exponential growth. However, the length of stationary phase in reciprocal bioreactor was longer than that in both the rotary bioreactors. Viability in 6FT and EE rotary bioreactors went to less than 90% (~ 130 h), faster than that in reciprocal bioreactor (160 h, Fig. 2A). Concentrations of glucose, lactate, and leaked lactate dehydrogenase activity in culture medium are shown in Fig. 3. Significant difference in glucose consumption was not observed in any bioreactor (Fig. 3A). In our cases of batch culture, consumption rate of lactate was more than its production rate when cell growth entered the stationary phase (at approximately 80 h, Fig. 3B). However, the concentration of lactate in reciprocal bioreactor decreased faster than in other rotary bioreactors. This revealed that physiological conditions of cells in all bioreactors proceeded from the production to consumption of lactate in approximately 80 h, and at the same time something else also changed that caused the difference in viability during the late stationary phase. High concentration of lactate in culture medium is detrimental for viable cells. Therefore, the rapid consumption of lactate in reciprocal bioreactor might make conditions more feasible for maintaining high cell viability.